1. Field of the Invention
This invention relates generally to electrical connectors for connecting daughter cards to a backplane, midplane, harness card or the like (hereinafter referred to as a "mother board" or "mother card"). More particularly, the invention relates to a self-centering contact, high density connector for connecting a daughter card directly to the plated through holes of the mother card, where the high density connector may be configured as a standard connector, a zero insertion force connector (ZIF) or as a sequential/selectively engaging pin connector.
2. Prior Art
The electrical connector arts are crowded arts with many categories and subcategories of connectors. One such category are connectors which are used to connect two printed circuit boards (PCB). Within that category is a subcategory of connectors where the first PCB is a mother board, and the second PCB is a daughter board at right angles to the mother board, and the connection is a pluggable connection such that replacement or cards and/or expansion of the system is easily accomplished. The standard connectors for permitting such a non-permanent right angle interface require placing a first piece of hardware (e.g. in the case of conventional inverted DIN connectors, the pin or male part) on the mother board, and a second piece of hardware (e.g. the mating female receptacle of a right angle connector) on the daughter board. While such connectors are typically successful for their purpose, as these connectors grow in size with high pin counts, bowing may occur in the connector during mating due to the high insertion force required resulting in difficult mating between the male and female connector shells. Further, these standard connectors are costly as they essentially require the use of two connector parts (a mating pair) for accomplishing a single connection. In fact, systems are often sold with the mother board portion of numerous connectors already attached to the mother board where daughter cards are only to be optionally provided in the event the system is expanded. Thus, where daughter cards are not ultimately used, unnecessary cost is suffered. In any event, it is desirable to provide an arrangement where connectors fixed to a daughter card could make electrical contact with the mother board directly without the added cost of a mating pair.
One solution to such a mother board/daughter board connection is proposed in U.S. Pat. No. 4,533,203 to Feldman et al., where a single connector having pins which are bent through a ninety degree turn and a two piece dielectric housing for housing the same are utilized in conjunction with contact pads on the mother board to establish contact. First ends of the pins are fixed to the daughter card while second ends are disposed at an oblique angle relative to the mother board to provide "wipe" action on the mating surface. Contact with the mother board is made between the angled second ends and contact pads on the mother board and aligning means are provided for aligning the angled pins and the pads. When contact is made, the bent portion of the pins deflects away from the mother board surface, and is permitted to do so by the housing which is enlarged around the area of deflection. With the provided arrangement, the two connector arrangement is obviated.
While the Feldman et al. patent does overcome some of the problems in the art, it does not address several matters of importance. First, the patent does not provide an adequate manner of maintaining the contact between the connector and the mother board, particularly where contact density is high. While a "keying block" is provided to establish alignment and to permit keying, there is no indication that the keying block also provides a means for establishing and maintaining contact. Second, because of the geometric nature of the angled pins and the contact pads, it is very possible that good contact at a sufficient contact force ("normal force") is not establishable between the pins and the circuit board. Third, where contact density is high, the size of the "engagement" or "hold-in" force (also called "mating" or "insertion" force) necessary for holding down the daughter board so that it may be locked relative to the mother board may very well be prohibitive. This is so, because the Feldman et al. configuration transmits the spring force directly to the contact pad on the mother card without any mechanical advantage. Thus, the "hold-in force" which is equal to the spring force, is also equal to the normal force. Fourth, because of the geometry and nature of the keying block, precise geometries are required, and if not met, may result in malfunctioning of the connector.